This invention relates generally to aircraft tire pre-rotation devices. More specifically, but without limitation, the present invention relates to an expendable, flexible, strap-on wheel acceleration system for vehicles, such as the Space Shuttle, which is attached to the tire before launch and is automatically deployed to rotate the tire when the tire is lowered into the airstream prior to touchdown.
It is well known that aircraft tires are subjected to tremendous stresses, especially at the moment of touchdown when the wheel must be accelerated to a circumferential velocity equal to the landing speed. When the tire contacts the ground, a cloud of smoke attests to the frictional acceleration that occurs. To make matters worse, this frictional acceleration occurs simultaneously with the imposition of high tire compressive forces due to the mass of the aircraft slamming to the runway surface. The tires slip and scuff, resulting in rapid, extreme heat buildup, rapid and uneven tire wear and some loss of directional stability. The problem becomes more acute with vehicles such as the Space Shuttle due to the high approach velocity (250 mph). In addition, the need to minimize weight is critical since the Space Shuttle must be launched into space.
To solve the problem, various means have been employed to pre-rotate the tires before touchdown to minimize the velocity differential. U.S. Pat. Nos. 3,428,274 and 2,404,018 use active means remote from the tire, such as motors, to pre-rotate the tires via gear drives. U.S. Pat. Nos. 3,797,786, 4,383,665, 3,529,792 and 4,205,812 use passive means attached to the sides of the wheels or tires to catch the wind and pre-rotate the tires. Still others, such as U.S. Pat. Nos. 3,773,283, 2,417,466 and 2,403,309 utilize passive means incorporated into the tire tread or tire rain grooves to catch the wind and pre-rotate the tires.
However, these devices are either heavy and cumbersome or do not provide sufficient rotational torque to attain a high enough rotational velocity. In addition, systems employing elements located on the tire tread are inadequate as they produce high vibrations and loss of directional stability when large enough to pre-rotate the tires to adequate velocities. In addition, they contribute to rapid tire wear and heat build-up.